The present invention relates to a method for driving a flat-panel display, and particularly to a method for driving a memory-type plasma display panel.
Among flat-panel displays, a plasma display panel which is generally a matrix-type display device connected to a column, is driven one line at a time. Thus, as compared with being driven one pixel at a time, the light-emitting time per line increases as much as the product of the number of data lines and the light-emitting time of each data bit, thereby enhancing brightness by extending the light-emitting time. In such display panels, since the device's efficiency of a DC-type color plasma display panel is inferior to a monochrome plasma display panel, its brightness degrades by line at a time driving as the monochrome plasma display panel. As one solution of this problem, methods for extending light emitting time within one field have been suggested, and a "memory system" can be given as an example of one solution. The term, "memory system" refers to the operating system of a plasma display panel which enhance the brightness by prolonging the light-emitting time, wherein once turned on, a cell is on continuously for one field or one subfield. That is, writing and erasing are performed for a vertical scanning period in the plasma display panel of line at a time driving, but the cell turned on during a vertical scanning period is continuously in the "on" state during the following vertical scanning period in the memory system.
Generally, in consideration of the need for high voltage to turn on a display tube, once the display tube is turned on, it can be continuously discharged at a lower voltage.
Here, the DC-type plasma display panel of the memory system will be described in detail. The DC-type panel uses "space charge" different from an AC-type panel which uses "wall charge".
FIG. 1 illustrates the current-to-voltage characteristic graph of a DC memory-type plasma display panel.
In FIG. 1, the dotted line has a negative resistance characteristic, and the memory of the DC-type plasma display panel starts to be operated by this characteristic. In more detail, when a cell having the characteristics shown in FIG. 1 is in the "off" state, it is turned on by a voltage greater than a discharge firing voltage V.sub.B. In contrast, when the cell is in the "on" state, it is turned off by a voltage below a minimum discharge sustaining voltage Vs. That is, the cell which goes over discharge firing voltage V.sub.b stays "on" state by applying a voltage V (provided that Vs&lt;V&lt;V.sub.B). By continuously applying this voltage, cells are capable of being controlled to maintain their on/off state. In addition, the turned-off cell can be turned on by applying a greater voltage than discharge firing voltage V.sub.B.
By the way, the above-referenced voltage (Vs&lt;V&lt;V.sub.B) is pulsed, because when a plurality of cells are simultaneously driven by the constant voltage under unloading state, excessive current flows, and when each cell carries a load, its efficiency is inferior to pulse discharge, and too much power is consumed. Also, writing and erasing become impossible.
FIG. 2A is a DC-type memory system, which represents the system of NHK Technological Institute of Japan.
Here, an auxiliary anode Al is arranged with a main anode A.sub.2 on the identical plane, so one auxiliary discharge cell C.sub.1 supplies priming particles to two display discharge cells C.sub.2. A constant current source is connected to auxiliary anode A.sub.1.
FIG. 2B illustrates the output waveform of driving circuit shown in FIG. 2A, of which operation is described below.
In accordance with the sequential scanning of cathodes K, auxiliary discharge cell C.sub.1 is discharged, so that the priming particles are always able to be supplied at the main discharge space. At this time, if the writing is carried out by generating the main discharge, the cell is discharged by allowing cathode K.sub.1 to load a writing pulse before a sustaining pulse. After that, since the sustaining pulse is continuously applied, the discharge also continues. Here, the sustaining pulse and scanning pulse do not overlap each other, whereby the cell in which the writing discharges once, continuously discharges, and the cell which has no writing discharge also remains unlighted.
That is, auxiliary anode A.sub.1 is for supplying the priming particles, main anode A.sub.2 is for writing and sustaining, and cathode K is for writing and erasing.
Therefore, the following problems occur.
First, auxiliary discharge cell C.sub.1, unnecessary to write, and display discharge cell C.sub.2 are arranged on the same plane, which is unsuitable for achieving higher resolution.
Second, since main anode A.sub.2 performs not only a writing operation but also one of sustaining, the increase of the line resistance of main anode A.sub.2 causes a problem. This is because all cathodes beneath the main anode are turned on in the memory-type, and thus too much current flows toward a main anode to cause a voltage-drop and the operational margin is decreased. Practically, indium-tin oxide and nickel cause such a problem due to their great line resistance, and although the resistance of gold or silver is good enough, a short may occur due to mercury.
Third, when a plurality of cells below a single anode are turned on, the output impedance of the driving circuit should be low, and its driving waveform is also complicated.